The present invention generally relates to the field of portable illumination devices for illuminating an ambient environment. More specifically, the present invention is directed to a hand-held laser flashlight which illuminates an ambient environment while minimizing the risk of causing irreversible eye damage.
Law enforcement, corrections, and military personnel face increasingly greater threats in their daily activities. Routine traffic stops can end in officers finding themselves in life-threatening situations. Domestic disputes and drug enforcement activities are amongst the most dangerous law enforcement personnel face. Also, increasingly law enforcement personnel face situations such as riots or unruly groups of individuals where certain lethal options cannot be used or would only serve to further exacerbate the situation. The availability of non-lethal weapons expands the range of options available to law enforcement in reacting to potentially violent or life-threatening situations.
Hand-held flashlights have been in widespread usage in many areas for many years. For example, in the area of forensics, law enforcement personnel have found flashlights to be so useful that incandescent flashlights have become "standard issue." These "standard issue" flashlights produce a bright beam from a small and relatively light-weight package. Such "standard issue" flashlights have, inter alia, been used by law enforcement personnel to illuminate crime scenes, to disorient and confuse suspects and to physically subdue suspects.
The effect of laser light on human eyesight can be separated into three categories: glare effects, dazzling or flashblinding, and permanent damage. The retinal damage threshold in general depends upon the laser wavelength, the exposure duration, and whether or not the laser is operated in continuous wave or pulsed or modulated mode and, if pulsed, the repetition rate and the pulse duration. If the laser light intensity is such that the damage threshold for the eye is exceeded, lesions are produced that are permanent. This damage occurs at the location of the retina for visible and near-infrared light. Ultraviolet and far-infrared light on the other hand are absorbed in the cornea and the light never reaches the retina.
The exact intensities where glare stops and dazzling occurs are difficult to define with precision and depend to a large extent on the individual involved. In general, however, glare occurs first and results in little or no loss of vision performance. In fact, after a laser source is turned off, in the glare region no after-effects or latent images occur. If the intensity is increased, however, at some intensity or over a range of intensities, dazzling occurs. If the laser is turned off, short-term partial loss of vision occurs, typically lasting for seconds or tens of seconds. At still greater intensities the after-effect is substantially longer, perhaps as long as minutes. This effect is best compared to the use of a fundus camera to photograph the retina of the human eye, usually under fully dilated conditions. Substantial vision loss can occur and last for many minutes.
Some inroads have also been made in applying laser technology to portable illumination devices in limited areas. One major drawback of such uses of lasers has been that the laser beam emitted by such low-power devices has the potential to produce irreversible eye damage if a person gazes directly into the light source. Thus, these devices are not "eyesafe." Naturally, this problem becomes exacerbated as attempts are made to increase the output power of such devices. Another significant limitation associated with such portable laser emitting devices is that they have, to date, been unable to produce nearly as much light as comparably sized incandescent flashlights. Accordingly, their lack of versatility and overall poor performance has limited their use.